In an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) of a third-generation mobile communication Long Term Evolution (LTE) system, uplink data is transmitted through a Physical Uplink Shared Channel (PUSCH). Uplink radio resources are allocated to each User Equipment (UE) by an Evolved NodeB (eNB). An access technology adopted by the E-UTRAN system is an Orthogonal Frequency Division Multiplexing (OFDM) technology. Compared with a second-generation mobile communication system, the radio resource management of the E-UTRAN system is featured with a wide bandwidth and multiple time courses, and the radio resources are two-dimensional time-frequency resources, thus greatly increasing the number of users carried therein.
A Radio Resource Control (RRC) layer of the LTE system may send an RRC message to realize many operations including establishing an RRC layer link between a UE and an eNB, configuring system parameters and transmitting UE capability parameters etc. A downlink RRC message is sent on a Physical Downlink Shared Channel (PDSCH). Some system-related common parameters, such as a cell frequency point and a cell system bandwidth and other information, are sent by the eNB to UEs in all cells through a broadcast message which is sent on a Physical Broadcast Channel (PBCH).
In order to allocate resources and provide services for every UE according to the demand thereof to realize a better multiplexing performance in uplink transmission, and fully, flexibly and efficiently utilizing the system bandwidth, the LTE system designs a special control message for allocating uplink transmission resources for a user. A special control message for allocating resources for the PUSCH is sent by the eNB to the UE; the resource allocation control message is also called UpLink Grant (UL Grant) which is sent on a Physical Downlink Control Channel (PDCCH).
In order to reasonably allocate radio resources for every UE, the LTE system requires the UEs to report the status of data volumes stored in their respective buffers and the report is reported to the eNB in the form of a Buffer Status Report (BSR). In the LTE system, Logical Channels (LCH) of a UE are divided into 4 Logical Channel Groups (LCG). The BSR reports the group number of every LCG and information of data volumes to be transmitted of all LCHs in the group. The BSR is carried by a PUSCH.
In the LTE system, a time interval for data transmission on a radio link is called a Transmission Time Interval (TTI).
Since the BSR is important reference information according to which the eNB performs reasonable radio resource scheduling for a UE, the LTE system stipulates many BSR types and sending rules. According to the varieties of events triggering the BSR, the BSR has three types, namely a Regular BSR, a Periodic BSR and a Padding BSR.
Trigger conditions of the Regular BSR include:
arrival of upper layer data that can be transmitted of a logical channel with a high priority which is higher than the priority of LCH data currently stored in a UE buffer;
change of a service cell; and
timeout of a BSR retransmission timer (RETX_BSR_TIMER), and the existence of data that can be transmitted in a UE buffer.
A trigger condition of the Periodic BSR is timeout of a Periodic BSR Timer.
A Trigger condition of the Padding BSR is that there is neither a Regular BSR nor a Periodic BSR to be sent and that the number of bits used for padding in allocated uplink PUSCH resources is greater than or equal to the sum of the size of a BSR MAC CE and the size of an MAC sub-header of the BSR MAC CE.
The Padding BSR is a filled-type BSR, which is a supplement to the Regular BSR and the Periodic BSR. Correspondingly, the Regular BSR and the Periodic BSR are non-filled type BSRs. When the uplink does not send a Regular BSR or a Periodic BSR, the padding BSR can more effectively enable the eNB to acquire an LCG data change in the UE buffer in time.
The carrying modes of the Regular BSR, the Periodic BSR and the Padding BSR are different, the Regular BSR and the Periodic BSR are respectively encapsulated as an MAC Control Element (CE) in a Media Access Control Protocol Data Unit (MAC PDU). The Padding BSR is carried in the padding bits of the MAC PDU and also encapsulated as an MAC CE. The only difference in the carrying modes of these three BSRs is the use of the padding bits. The MAC PDU is sent on a PUSCH.
According to the definition of the current protocol standard (3Gpp TS36.321) of an LTE MAC layer, the structure of the aforementioned MAC PDU is as shown in FIG. 1. One MAC PDU comprises an MAC header, 0, 1 or more MAC CEs, 0, 1 or more MAC Service Data Units (SDU) and an optional padding bit (Padding). The MAC header comprises multiple MAC sub-headers, each of which is corresponding to the MAC CE, the MAC SDU or the Padding arranged after the MAC header in order. The MAC sub-headers include information such as the length or format of the corresponding MAC CE, the MAC SDU or the Padding. One MAC SDU at most includes one BSR MAC CE.
According to the format applied when a BSR is sent, the BSR has three types, namely a short BSR, a truncated BSR and a long BSR. According to the definition of the protocol standard of the LTE MAC layer, as shown in FIG. 2 and FIG. 3, the BSR format as shown in FIG. 2 is called a short BSR or a truncated BSR and the BSR format as shown in FIG. 3 is called a long BSR format. When a BSR triggered by a UE is a Regular BSR or a Periodic BSR and there is data to be transmitted in only one LCG of the UE in a TTI to send the BSR, the UE adopts a short BSR format to send the BSR. When a BSR triggered by a UE is a Regular BSR or a Periodic BSR and there is data to be transmitted in multiple LCGs of the UE in the TTI to send the BSR, the UE adopts a long BSR format to send the BSR. When a BSR triggered by a UE is a Padding BSR and there is data to be transmitted in multiple LCGs of the UE in the TTI to send the BSR, and the length of padding bits of the MAC PDU is insufficient to send a long BSR and a corresponding MAC sub-header, the UE adopts a truncated BSR format to report the BSR. When a BSR triggered by a UE is a Padding BSR, and there is data to be transmitted in multiple LCGs of the UE in the TTI to send the BSR, the UE reports the BSR by adopting a short BSR format. It should be noted that although the short BSR and the truncated BSR apply the format as shown in FIG. 2, they represent different meanings.
After a Regular BSR is triggered by a UE, since the events triggering the BSR are important events, the UE needs to trigger a scheduling request (SR) if there are no PUSCH resources for the UE in the present TTI to send the BSR. When there are available PUSCH resources for the UE in a subsequent TTI to send the BSR, the SR will be cancelled. When there are no available PUSCH resources for the UE in a subsequent TTI to send the BSR, the SR will be sent to the eNB on PUCCH resources to require the eNB to allocate PUSCH resources for the UE.
According to the definition of the current protocol standard (3Gpp TS36.321) of the LTE MAC layer, the basic flow of triggering and sending a BSR is as follows:
in each TTI, the UE determines whether to trigger a BSR according to the aforementioned BSR trigger conditions;
in each TTI, the UE determines whether there is a triggered BSR; if yes, the UE further determines whether there are available PUSCH resources in the current TTI and if there are available PUSCH resources in the current TTI, an appropriate BSR format is selected and encapsulated as an MAC CE; if there is no triggered BSR, the UE further determines whether to trigger a Padding BSR, if yes, an appropriate BSR format is selected and encapsulated as an MAC CE. After an MAC PDU is packaged, uplink transmission is performed.
The definitions of the aforementioned BSR formats and sending rules are defined in the current LTE release 8 standard. In order to adapt to the rapid increase in the demands of radio services at present and in the future, the next evolved LTE release 8 standard, namely an LTE-Advanced standard, is being formulated.
The LTE-Advanced is a standard put forward by the 3rd Generation Partner Project (3GPP) to meet the requirements of the International Mobile Telecommunication-Advanced (IMT-Advanced) of the International Telecommunication Union (ITU). An LTE-Advanced system is an evolved edition based on an LTE release 8 system. The LTE-Advanced system introduces many new technologies to meet the basic demands of the IMT-Advanced and the most important one is carrier aggregation.
Because of the shortage of radio frequency spectrum resources, the radio frequency spectrum resources owned by mobile operators all over the world are relatively scattered and the IMT-Advanced requires a higher peak rate (supporting 100 Mbps at high mobility and supporting 1 Gbps at low mobility). The maximum bandwidth of 20 MHz in the current LTE standard cannot meet the requirement of the IMT-Advanced, thus it is necessary to extend the bandwidth to a wider one, such as 40 MHz, 60 MHz or even wider. One of the methods to increase the bandwidth and the peak rate is to extend a frequency domain, that is, several frequency bands are bound to extend the bandwidth by means of carrier aggregation, which is the essence of the carrier aggregation technology.
In the LTE-Advanced system applying the carrier aggregation technology, the carrier participating in aggregation is called a component carrier. A UE can perform receiving and sending transmission with an eNB in multiple frequency bands at the same time and still maintain the properties of the LTE release8 in a single frequency band, that is, the LTE-Advanced can be viewed as being formed by “binding” multiple LTE systems.
After introducing the carrier aggregation technology, the available resources of the LTE-Advanced system is greatly extended and the flexibility of uplink scheduling is largely improved, the eNB can allocate resources for a UE in the frequency band of every component carrier.
The LTE-Advanced system can support a maximum uplink transmission bandwidth of 100 MHz and a maximum number of layers of 4 of uplink spatial division multiplexing (the maximum number of layers of uplink spatial division multiplexing supported by the LTE release 8 system is 2), therefore a maximum buffer data volume supported by a UE in the LTE-Advanced is theoretically 10 times as much as that of a UE in the LTE system, the LTE-Advanced thus requires a greater number of bytes to report a BSR. In addition, there maybe a plurality of available component carriers on an uplink of a UE of the LTE-Advanced at the same time, there have not provided specific rules and methods of sending a BSR on a plurality of component carriers. A BSR sending mechanism of the current LTE system is only applicable to a single-carrier system, which cannot meet the demand of the LTE-Advanced system. If the LTE-Advanced system follows the BSR sending mechanism of the LTE system, a BSR will be sent on one component carrier. Because of the difference of the channel quality of different component carriers, the rate of correctly sending a BSR cannot meet the requirement of the LTE-Advanced system when the BSR is sent on only one component carrier. In addition, it will result in large overheads of the system if the BSR is sent on all component carriers. Therefore, the design and the sending mechanism of a BSR in the LTE-Advanced should take both the correct rate and the overheads into consideration.
In the current LTE system, channel quality difference-related information sent by an eNB to a UE is only a Modulation and Coding Scheme (MCS). Every MCS corresponds to a unique combination of a modulation mode and a coding rate. The higher MCS will have a corresponding higher modulation mode or a higher coding rate. Since high communication quality can be achieved only when a higher modulation mode or a higher coding rate are applied to a radio channel with higher quality, normally, the eNB will apply a higher MCS to component carrier radio resources with higher channel quality. In the LTE-Advanced system, there maybe more channel quality difference-related information sent by the eNB to the UE.
In addition, since the maximum buffer data volume supported by a UE in the LTE-Advanced system is far more than that supported by a UE in the LTE system, the current BSR design of the LTE system cannot meet the demand of the LTE-Advanced UE and new BSR types should be designed according to the characteristics of the LTE-Advanced system. Furthermore, since the LTE-Advanced system should maintain the backward compatibility with an LTE UE, the LTE-Advanced system may include both an LTE UE and an LTE-Advanced UE, as well as both BSR types in the LTE and new BSR types; therefore it remains a problem for a network side to distinguish whether a BSR sent by a UE is of a BSR type in the LTE or of a new BSR type.
Therefore, in regard to the aforementioned problems, a method, a corresponding terminal and system for reporting a buffer status report in a system adopting a carrier aggregation technology are required to increase the rate of correctly sending a buffer status report while saving uplink radio resources.